1. Field of the Invention
The present invention relates generally to the field of solid-state white lighting devices and specifically to the field of high-brightness lighting, in which there is a need to illuminate a large area. In particular, the invention embodies the generation of white light using a laser diode (LD) as the excitation source in combination with phosphor materials for high-brightness applications.
2. Description of the Related Art
Large area venues such as sports arenas, auditoriums, and parking lots require a lighting system with high brightness, high luminous efficacy, and quality white light in terms of color rendition and color temperature. The lighting system should additionally have the qualities of energy efficiency, simple and flexible operation and control, easy and low-cost maintenance, and environmental sustainability.
Most current high-brightness lighting systems use high intensity discharge (HID) lamps, which are usually metal halide or high pressure sodium vapor lamps. These HID lamps are widely used for this application due to their high luminous efficacy compared to fluorescent or incandescent lamps and longer operating lifetimes. A typical metal halide lamp has a luminous efficacy of 65 lm/W to 115 lm/W with a lifetime of 10,000 hours to 20,000 hours. The quality of the white light produced is also suitable for large venue applications with a color rendering index (CRI) of 65 to 90 and a correlated color temperature (CCT) of 3000 K to 20,000 K. The HID light fixtures are typically mounted at a distance above the venue and the output light is directed to illuminate the area below.
The use of HID lamps for high-brightness lighting applications currently poses a number of disadvantages. For one, the warm up time for the lamps to reach full brightness can take anywhere from 1 minute to 15 minutes. Additionally, if the lights are turned off, it can take up to 10 minutes before they can be turned on again. This cycling of restarting the lighting before they have sufficiently cooled is also a source of wear and leads to quicker degradation and shorter lifetimes. For this reason, large venue lighting is rarely turned off if the lights need only to be off for a short amount of time. In this case, shutters are used to block the light, instead of turning the lights off. This is not an energy efficient means of operation since electricity is still being used by the lights. The same situation occurs if only a section of lights is to remain on during an event. This operation technique therefore also introduces a shutter into the lighting system, which must also be maintained and may require a motor for operation. The final disadvantage of HID lamps for large venue lighting concerns the maintenance. Replacement of lights requires manual replacement, and since the lamps are usually mounted at a height above the venue, this can be a dangerous task.
With the advent of light emitting diode (LED) technologies, such as laser diodes, new large venue lighting systems are being designed. These include the use of LEDs combined with a phosphor material to produce white light. LED-based lamps offer similar benefits as HID lamps in terms of luminous efficacies, color rendition, and color temperature. LED-based lamps also have the advantage of longer lifetimes up to 50,000 hours, relatively instant turn-on times achieving full brightness in less than a microsecond, the ability to be turned off and on quickly, and environmental sustainability. An important advantage is therefore that different sections of lights can be flexibly turned on and off at will, eliminating the need for shutters and saving energy. The maintenance problems still exist with LED-based stadium lighting as with HID lamps, such that replacement requires individual bulbs to be changed manually.
There is therefore a need for large venue lighting that includes all of the benefits of prior systems including high-brightness, high efficiency, high luminous efficacy, long lifetimes, quick turn-on times, suitable color properties, and environmental sustainability with the added advantage of easy maintenance. Such a system would allow for smart and flexible control over the lighting, ease of maintenance, and savings in operating and maintenance costs. The present invention satisfies this need.